1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and a method for manufacturing the LCD and more particularly to the LCD made up of unit pixels each having two driving elements driven by a same scanning line and two pixel electrodes to one of which a pixel voltage fed from one of two data lines is applied through one of the driving elements and to the other of which a pixel voltage fed from the other of the two data lines being opposite in polarity to the pixel voltage fed from the former of the two data lines is applied through the other of the driving elements and the method for manufacturing the above LCD.
The present application claims priority of Japanese Patent Application No.2001-085545 filed on Mar. 23, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
An LCD is widely used as a display for various information devices. The LCD is basically so configured that a liquid crystal is put in a hermetically sealed manner between a TFT (Thin Film Transistor) substrate (driving element substrate) on which a TFT is formed serving as a switching element (driving element) used to do ON/OFF switching for selection of each of unit pixels to provide a display on a screen and a facing substrate and that a plurality of unit pixels is arranged in a matrix form. Such the LCD is roughly classified, according to a difference in its display method, into a TN (Twisted Nematic)-type LCD and an IPS (In-Plane Switching)-type LCD.
In the TN-type LCD, a pixel voltage is applied to a pixel electrode formed on a TFT substrate and a common voltage is applied to a common electrode formed on a facing substrate and, by a difference between the pixel voltage and the common voltage, a longitudinal electric field is generated in a direction orthogonal to surfaces of both the TFT substrate and the facing substrate to drive a liquid crystal.
On the other hand, in the IPS-type LCD, both a pixel electrode and a common electrode are formed on a TFT substrate being one of two substrates in such a manner that both the pixel electrode and the common electrode are insulated from each other by an interlayer insulating film and, by a difference in voltages between the pixel electrode and the common electrode, a transverse electric field is generated in a direction horizontal to surfaces of both the pixel electrode and the common electrodes to drive a liquid crystal.
When the LCD is driven by the method described above, the IPS-type LCD in particular, has an advantage in that, since a longitudinal axis of its liquid crystal molecule is arranged in a horizontal direction along the surfaces of both the TFT substrate and facing substrate, a change in brightness is made small even by a change of viewing direction when the LCD is observed and it can provide a wide viewing angle. Therefore, in recent years, there is a tendency that the IPS-type LCD is preferably used.
FIG. 35 is a plan view showing configurations of a conventional IPS-type LCD. FIG. 36 is a cross-sectional view of FIG. 35 taken along a line Lxe2x80x94L. In FIGS. 35 and 36, configurations of one unit pixel 100 only are shown. As shown in FIGS. 35 and 36, a liquid crystal 103 is put in a hermetically sealed manner between a TFT substrate 101 and a facing substrate 102. The TFT substrate 101 includes a first transparent substrate 106 made of glass or a like, a first polarizer 107 formed on a rear of the first transparent substrate 106, a scanning line (gate bus line) 108 formed on apart of a surface of the first transparent substrate 106, common electrodes 109 formed on an other part of the surface of the first transparent substrate 106, an interlayer insulating film 110 serving as a gate insulating film formed in a manner so as to cover the scanning line 108 and the common electrodes 109, a semiconductor layer 113 formed on the scanning line 108 with the interlayer insulating film 110 being interposed between the semiconductor layer 113 and the scanning line 108, a drain electrode 116 and a source electrode 117 each being connected to the semiconductor layer 113, pixel electrodes 121 and data lines 122 formed on the interlayer insulating film 110 being integrated into the drain electrode 116 and the source electrode 117, a passivation film 125 formed in a manner so as to cover the pixel electrodes 121 and the data lines 122, and a first oriented film 127 formed in a manner so as to cover the pixel electrodes 121 and the data lines 122 with the passivation film 125 being interposed between the first oriented film 127 and the pixel electrodes 121 and the data lines 122. Here, the scanning line 108, semiconductor layer 113, drain electrode 116 and source electrode 117 make up a TFT 129.
On the other hand, the facing substrate 102 includes a second transparent substrate 131 made of glass or a like, a second polarizer 133 formed on a rear of the second transparent substrate 131 with a conductive layer 132, for prevention against static electricity, being interposed between the second transparent substrate 131 and the second polarizer 133, a black matrix layer 134 formed on a surface of the second transparent substrate 131, a colored layer 135 serving as a color filter formed in a manner so as to cover the black matrix layer 134, a planarized film 136 formed in a manner so as to cover the black matrix layer 134 and the colored layer 135, and a second oriented film 137 formed on the planarized film 136. The arrow line 139 shows an oriented direction of the liquid crystal 103.
In order to drive the conventional LCD as described, a voltage having a different polarity by every period is cyclically applied to pixel electrodes 121 making up a unit pixel 100, with an aim to increase a life of a liquid crystal 103. That is, a pixel voltage Ve having a different polarity by every period as shown in FIG. 37 is fed to the pixel electrodes 121 through the TFT 129 from the data lines 122. In FIG. 37, a common voltage Vc is applied to the common electrodes 109 and the liquid crystal 103 is driven by voltage differences Vd1 and Vd2 between the pixel voltage Ve and the common voltage Vc with timing when a scanning voltage (not shown) is fed and the liquid crystal 103 holds an electric charge corresponding to each of the voltages for driving the described above.
To drive the liquid crystal 103 by cyclically feeding the pixel voltages Ve each having a different polarity by each period to the pixel electrodes 121, three methods described below are mainly employed. A first method is called a xe2x80x9cone-horizontal-reverse driving methodxe2x80x9d in which, to switch image data making up an image in a display, a polarity of the unit pixel 100 is reversed from a positive side to a negative side and vice versa for every one horizontal line of unit pixels 100, as shown in FIG. 38A. A second method is called anxe2x80x9cone-vertical-reverse driving methodxe2x80x9d in which, to switch the image data, the polarity of the unit pixel 100 is reversed from a positive side to a negative side and vice versa for every one vertical line of unit pixels 100 as shown in FIG. 38B. A third method is called a xe2x80x9cdot-reverse driving methodxe2x80x9d in which, to switch the image data, a polarity of the unit pixel 100 is reversed from a positive side to a negative side and vice versa for every dot in such a manner that unit pixels 100 are displayed checkerwise as shown in FIG. 38C.
FIG. 39 is a diagram showing a driving circuit employed in the conventional LCD and FIG. 40 is an expanded diagram showing a terminal section A shown in FIG. 39 and a terminal section B shown in FIG. 39. As shown in FIG. 39, a scanning line driving circuit 151 is connected to a scanning line 108 making up the unit pixels 100 being arranged in a matrix form and a scanning line signal is fed to each of the unit pixels 100 through the scanning line 108, while a data line driving circuit 152 is connected to data lines 122 and a data line signal is fed to the unit pixel 100 through the data lines 122. Moreover, a common electrode wiring driving circuit 153 is connected to a common electrode wiring 120 and a common voltage Vc is fed to the unit pixel 100 through the common electrode wiring 120.
As is apparent from FIG. 40, in the terminal section A, each of data line terminal sections 122A adapted to supply a potential to the data lines 122 is coated with an ITO (Indium Tin Oxide) film 122a. Moreover, in the terminal section B, a scanning line terminal section 108A adapted to supply a potential to the scanning line 108 is coated with an ITO film 108a and a common electrode wiring terminal section 120A adapted to supply a potential to the common electrode wiring 120 is coated with an ITO film 120a. 
However, the conventional LCD has a disadvantage in that, when a display by only the unit pixels 100 each having a same polarity on a screen is required, strong flicker occurs which causes an unclear display screen. For example, when pixels each having a positive polarity only as shown in FIG. 41A, or each having a negative polarity only as shown in FIG. 41B are displayed checkerwise, strong flicker occurs. This is because the conventional LCD is so configured that, by displaying a plurality of unit pixels 100 each being supplied with pixel voltages Ve each having a different polarity, occurrence of flickers is apparently reduced. More particularly, this is because an ON-characteristic of the TFT 129 being connected between the data lines 122 and the pixel electrodes 121 and a data voltage holding characteristic of the liquid crystal 103 are different depending on whether a polarity of a supplied voltage is positive or negative. That is, in FIG. 37, no problem occurs if the voltage differences Vd1 and Vd2 are equal to each other, however, since the common voltage Vc changes, the voltage difference Vd1 becomes different from the voltage difference Vd2 and, therefore, when the unit pixels 100 are displayed checkerwise, the occurrence of the strong flicker is inevitable.
A conventional LCD in which an attempt has been made to inhibit occurrence of strong flicker even when only the unit pixels 100 each having a same polarity are displayed is disclosed in, for example, Japanese Patent Application Laid-open No. 2000-235371. FIG. 42A is a diagram showing configurations of a circuit employed in the above conventional LCD. FIG. 42B is a layout diagram of the conventional LCD of FIG. 42A. The disclosed conventional LCD, as shown in FIGS. 42A and 42B, includes a scanning line 201c, a main data line 202c, a sub-data line 202d, a common wiring 209, a main TFT 203c being connected to a point of intersection between the scanning line 201c and the main data line 202c, a sub-TFT 203d being connected to a point of intersection between the scanning line 201c and the sub-data line 202d, facing electrodes 211, a main pixel electrode 204c, a liquid crystal 210c being put in a hermetically sealed manner between one of the facing electrode 211 and the main pixel electrode 204c, a liquid crystal 210d put in a hermetically sealed manner between another of the facing electrode 211 and a sub-pixel electrode 204d, a storing capacitor 208c formed between the common wiring 209 and the main pixel electrode 204c, and a storing capacitor 208d formed between the common wiring 209 and the sub-pixel electrode 204d. 
In the conventional LCD having configurations described above, for example, as shown in FIG. 38A, when image data making up images of pixels existing on one horizontal line is switched, by reversing a polarity of a pixel voltage to be fed to the main electrodes 204c to a positive side or a negative side and vice versa for every unit pixel 100 and to the sub-electrode 204d to a negative side or a positive side and vice versa, a pixel having a positive polarity and a pixel having a negative polarity both having a same luminance can be always disposed adjacent to each other for every unit pixel 100 and, therefore, even when only pixels each having a same polarity are displayed, it is possible to inhibit the occurrence of strong flicker.
However, in the disclosed conventional LCD, though, even when only pixels each having a same polarity are displayed, the occurrence of a strong flicker can be inhibited, there is a problem in that, since the main data line and sub-data line used to apply a pixel voltage having a positive or negative polarity and a pixel voltage having a negative or positive polarity to the main pixel electrode and sub-pixel electrode respectively in the unit pixel 100 are formed on a same plane and a decrease in an aperture rate of the unit pixel 100 occurs. That is, in the conventional LCD disclosed in the Japanese Patent Application Laid-open No. 2000-235371, as shown in FIGS. 42A and 42B, since the two kinds of the data lines, one being the main data line 202c used to feed a pixel voltage to the main pixel electrode 204c through the main TFT 203c and another being the sub-data line 202d used to feed a pixel voltage to the sub-pixel electrode 204d through the sub-TFT 203d, are formed on a same plane, an area occupied by the data lines in the unit pixel 100 is doubled, which causes a decrease in an area through which light transmits and therefore a decrease in the aperture rate.
In the case of the IPS-type LCD in particular, as shown in FIGS. 35 and 36, since the common electrodes 109 and the pixel electrodes 121 both being made from light-shielding metal are mounted on a same plane, its aperture rate is originally low. Therefore, if such configurations shown in FIGS. 42A and B are employed in the IPS-type LCD, the aperture rate becomes worse, which makes it difficult to achieve a bright display by an LCD.
In view of the above, it is an object of the present invention to provide an LCD and a method for manufacturing the LCD which are capable of inhibiting occurrence of a strong flicker even when only pixels each having a same polarity are displayed on a screen, without causing a decrease in an aperture rate.
According to a first aspect of the present invention, there is provided an LCD including:
A plurality of unit pixels each having a liquid crystal being put in a hermetically sealed manner between a driving element substrate on which driving elements are formed and a facing substrate wherein the driving elements are made up of first and second driving elements driven by a same scanning line, and having first and second pixel electrodes to one of which a pixel voltage is fed from one of the first and second data lines through one of the first and second driving elements and to the other of which a pixel voltage being opposite in polarity to the pixel voltage fed from the one of the first and second data line is fed from the other of the first and second data lines through the other of the first and second driving elements;
wherein the first and second data lines are formed in a manner that the second data line is disposed above the first data line and in a manner that the first data line is overlaid by the second data line with an insulating film being interposed between the first and second data lines on the driving element substrate.
In the foregoing, a preferable mode is one wherein the insulating film is constructed of an organic insulating film or an inorganic insulating film or a stacked layer made up of both the organic insulating film and the inorganic insulating film.
Also, a preferable mode is one wherein the first and second pixel electrodes and common electrodes are formed on the driving element substrate in a manner that the first and second pixel electrodes and the common electrodes are insulated from each other by an interlayer insulating film.
Also, a preferable mode is one wherein the first and second pixel electrodes and the first data line are formed on a same insulating film.
Also, a preferable mode is one wherein the first and second pixel electrodes and the second data line are covered by an oriented film.
Also, a preferable mode is one wherein the first and second data lines both applying a pixel voltage having a same polarity are overlaid by each other.
Also, a preferable mode is one wherein the first and second data lines feed the pixel voltage to the first and second pixel electrodes in unit pixels being different from each other.
Also, a preferable mode is one wherein a colored layer is formed on the driving element substrate.
Also, a preferable mode is one wherein the common electrodes are in contact with the liquid crystal through the oriented film.
Also, a preferable mode is one wherein the second data line is formed in a manner that the second data line is disposed above the first data line and that the first data line is overlaid by the second data line with the interlayer insulating film being interposed between the second and first data lines.
Also, a preferable mode is one wherein the first and second pixel electrodes and the common electrodes are formed on the same interlayer insulating film covering the second data line.
Also, a preferable mode is one wherein the common electrodes are formed on the facing substrate.
Furthermore, a preferable mode is one wherein the unit pixel is driven by an one-horizontal-reverse driving method, an one-vertical-reverse driving method, or a dot-reverse driving method.
According to a second aspect of the present invention, there is provided a method for manufacturing an LCD including unit pixels each having first and second driving elements driven by a same scanning line and having first and second pixel electrodes to each of which a pixel voltage having a different polarity is applied from each of first and second data lines through each of the first and second driving elements, the method including:
a first process of forming a first interlayer insulating film in a manner that the first interlayer insulating film covers a scanning line after the scanning line has been formed on a transparent substrate and forming a semiconductor layer on the first interlayer insulating film;
a second process of forming a drain electrode and a source electrode on the semiconductor layer to form the first and second driving elements and forming the first and second pixel electrodes on the first interlayer insulating film and the first data line to be connected to the drain electrode of one of the first or second driving elements;
a third process of forming a contact hole in a second interlayer insulating film after the second interlayer insulating film has been formed in a manner that the second interlayer insulating film covers the driving element and forming the second data line to be connected to the drain electrode of another driving element through the contact hole in a manner that the first data line is overlaid by the second data line with the second interlayer insulating film being interposed between the first and second data lines.
In the foregoing, a preferable mode is one wherein, in the third process, as the second interlayer insulating film, an organic insulating film or an inorganic insulating film or a stacked layer made up of both the organic insulating film and the inorganic insulating film is formed.
With the above configurations, the first and second data lines each feeding a pixel voltage being different in polarity to each of the first and second pixel electrodes through each of the first and second TFTs are formed in such a manner that the first data line is overlaid by the second data line with the insulating film being interposed between the first and second data lines and therefore an area occupied by the data lines in a unit pixel can be reduced, showing no difference in the area to be occupied by the data line between the case of using two data lines and a case of using only one data line. Moreover, since known processes of forming thin films including conductive films and insulating films and known thin film patterning processes are used in combination, the LCD can be manufactured easily without causing an increase in costs. Therefore, even when only pixels each having a same polarity are displayed on a screen, an occurrence of strong flicker can be avoided without causing a decrease in the aperture rate.